Project Summary/Abstract ? Project 3 Type-1 diabetes (T1D) is a serious autoimmune disease, whose incidence has been steadily increasing in recent years. It results from an immune attack on the pancreas by the patients T cells that selectively eliminates the insulin-producing beta cells that reside in the organs Islets of Langerhans eventually. The risk of developing T1D is tied to both environmental and genetic factors. The main genetic factor is tied to the polymorphisms in the genes encoding Class II molecules within the major histocompatibility gene complex (MHCII). The usual function of MHCII molecules is usually to capture antigenic peptides derived from foreign proteins for presentation to and activation of CD4+ T cells in order direct these cells fight off infections. Since MHCII molecules can also capture and present peptides derived the host's own protein, the immune system has developed an elaborate two stage mechanism for preventing these self-peptides from inducing an autoimmune response against the hosts on tissues. The first stage involves a pre-check of CD4+ T cells in the thymus early in their development eliminating T cell whose antigen recognizing receptor (TCR) can engage an MHCII molecule containing a self-peptide. The second stage involves a set of regulatory T cells in the peripheral organs to deal with T cells that have somehow escaped the thymic pre-check. However, under the right conditions some of CD4+ T cells specific for certain peptides derived from pancreatic islet proteins sneak through both of these filters to cause T1D. The main objective of Project 3 is to determine why the T cells specific some pancreatic peptides are deleted in the thymus, while others are not, and to see if this information can be used to beef up the peripheral regulatory T cells to prevent the activation of the escapees. In Project 3 our main hypothesis is that the thymic escapees recognize peptides that bind poorly in the thymus to the relevant MHCII risk alleles and therefore break through the thymic first filter. We will test this hypothesis by altering the expression of various pancreatic peptides in the thymus to see what effect this has on the appearance of CD4+ T cells of those specificities. We will also test the idea that by engineering the relevant peptide to bind better to the MHCII risk alleles we can create a ?super agonist? that can be used to delete pathogenic T cells or to boost the activity of the peripheral regulatory T cells to prevent the activation of the pathogenic ones.